Bumper equipped with shock-absorbing means

ABSTRACT

A vehicle bumper with shock-absorbers, including a rigid support attached to a vehicle onto which a bumper shell is fitted, the shock-absorbers including at least two pyrotechnic actuators linking the rigid support to the vehicle, the actuators being connected for activation by a control system including an impact or deceleration sensor, and each pyrotechnic actuator including at least two gas-generating powder tablets to be primed individually by the control system.

FIELD AND BACKGROUND OF THE INVENTION

The technical scope of the invention is that of bumpers for vehicles,and notably for motor vehicles.

Existing bumpers do not allow impacts to be absorbed that occur when thevehicle is at a speed greater than 15 km/h without damage to the body.

So as to restrict the violence of frontal impacts it is known to designbumpers fitted with shock-absorbing means.

Thus, patents U.S. Pat. Nos. 3,822,076 and 3,708,194 show vehiclesfitted with an inflatable bag that is deployed to the front of thebumper in the event of sudden deceleration. This bag allows part of thekinetic energy to be absorbed and protects the vehicle's occupants.

Said devices employing deployable bags are complicated to implement. Toprotect the vehicle, the bag must have a substantial volume wheninflated and is thus not able to deploy both rapidly and reliably.Additionally, the folded bag must only occupy a small amount of space,its casing is therefore thin and not very strong. It will burst uponimpacting an obstacle and will therefore afford little protection.

Another problem with known systems lies in that they only provide asingle level of shock-absorption for the bumper. Said bumper istherefore not able to be suitably adapted to various situations whetherrelated to the intensity of impact or its position with respect to themedian axis of the vehicle.

An impact located on one of the sides of the bumper can thus be noted tocause the vehicle to wrap itself around the obstacle thereby seriouslyprejudicing the safety of the vehicle's occupants.

Patent U.S. Pat. No. 5,651,569 describes another device in which thebumper incorporates a reinforced rubber bag that is permanently inflatedby means of a compressible fluid and that is encased in a metal shell.

The bag is inflated when the bumper is mounted onto the vehicle and itallows the impacts received by the bumper to be distributed and absorbedby the compression of said fluid.

However, such a device suffers nevertheless from certain drawbacks.

Thus, the bag is likely to gradually deflate over time, thereby reducingits shock-absorbing capabilities.

Additionally, such a system provides a single level of shock-absorptionfor the bumper. It is therefore not able to be suitably adapted tovarious situations whether related to the intensity of impact or itsposition with respect to the median axis of the vehicle.

Patents DE19514191 and EP850807 describe bumpers that are attached tothe vehicle by means of pyrotechnically controlled actuators. Suchsystems are also unable to be suitably adapted to various situationswhether related to the intensity of impact or its position with respectto the median axis of the vehicle.

BRIEF SUMMARY OF THE INVENTION

Thus, the bumper proposed by the invention provides greatershock-absorbing capabilities that can be modulated according to theforce and/or position of the impact received.

The invention thus relates to a bumper for a vehicle fitted withshock-absorbing means, and comprising a rigid support linked to thevehicle onto which a shell intended to receive the impacts is fitted,said shock-absorbing means comprising at least two pyrotechnic actuatorslinking the rigid support to the vehicle, said actuators being activatedby a control system linked to at least one impact and/or decelerationsensor, said bumper being characterised in that each pyrotechnicactuator incorporates at least two gas-generating powder tablets able tobe primed individually by the control system so as to provide theactuator with at least two efforts of different intensities.

The control system will be advantageously linked to means allowing theposition of the impact received by the vehicle to be located withrespect to the median axis of the vehicle, and the control system willthen initiate the nearest actuator to the point of impact with a greatereffort than that transmitted to the actuator furthest away.

The impact-locating means will be advantageously constituted by thespacing of at least two impact sensors on either side of the median axisof the vehicle.

According to a first embodiment of the invention, the bumperincorporates at least one block of shock-absorbing material placedbetween the rigid support and the shell.

Each shock-absorbing block can be formed of hollow balls arranged in amatrix of plastic material, said balls being crushed under impact to theshell.

According to a second embodiment of the invention, the shock-absorbingmeans comprise at least one inner volume in the shell that can bepressurised by means of a compressible fluid supplied by at least onegenerator initiated by the control system linked to at least one impactand/or deceleration sensor.

Advantageously, the pressurizable volume can comprise at least onecasing made of an elastic material such as rubber, reinforced or not,the casing being arranged between the rigid support and the shell.

The casing can incorporate longitudinal and/or transversal partitionsdelimiting at least two inner cavities in the casing.

The fluid generator or generators intended to inflate the casing orcasings will preferably be pyrotechnic gas generators.

According to another embodiment, the device can incorporate two gasgenerators.

In this case, the control system will initiate one or other gasgenerator according to a different level of impact or deceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood after reading the followingdescription of the different embodiments, such description being madewith reference to the appended drawings, in which:

FIG. 1a is a longitudinal section view of a bumper according to theinvention;

FIG. 1b is a transversal section view of this same bumper along plane AAmarked out in FIG. 1a;

FIG. 2a is a longitudinal section view of a bumper according to a secondembodiment of the invention;

FIG. 2b is a transversal section view of this same bumper along plane BBmarked out in FIG. 2a;

FIG. 3 is a longitudinal section view of a bumper according to a thirdembodiment of the invention;

FIG. 4 is a longitudinal section view of a variant embodiment of thebumper according to the invention;

FIG. 5 is a transversal section view of another variant embodiment ofthe bumper according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1a and 1 b, a bumper 1 according to theinvention is arranged to the fore or rear of the vehicle, and comprisesa shell 2, made of a plastic or composite material, intended to receiveimpacts. This shell is fastened to a rigid support 3 by linking means,not shown in detail, and that can comprise, for example, severalsupports 4, evenly spaced longitudinally, riveted or bonded to theshell, and screwed to support 3.

The rigid support 3 is a bar, made of composite materials or steel, thatis linked to the vehicle chassis (not shown) by two arms 5.

The inner volume 7 of the shell 2 encloses several substantiallyparallelepiped blocks 19 of a shock-absorbing material formed by hollowballs (of metal or of a plastic material such as epoxy-based polymer) of12 to 15 mm in diameter, said balls being arranged in a resin matrix.

Such shock-absorbing blocks are well known to the expert, notably bypatents EP212712 and EP359769, and are not described hereafter in anyfurther detail.

In this example, the shell encloses eight identical shock-absorbingblocks separated into two groups. A first group of four blocks isarranged at the right side of the shell and a second group of fourblocks is arranged at the left side, the blocks being arrangedsymmetrically to each other with respect to the median axis 14 of thevehicle.

Each group 19 of blocks is placed opposite one of the arms 5.

Blocks 19 are fastened to the rigid support 3 by a rectangular baseplate 20 made of plastic or metal and having partitions 21 delimitinghousings for each block. The base plate is screwed onto support 3 andthe blocks are fitted into and can be bonded to base plate 20.

Blocks 19 are of a length such that their upper face presses against theinner wall of the shell 2.

Each arm 5 comprises a pyrotechnic actuator 9 that has a rod 9 afastened to the rigid support 3 and a body 9 b linked to the vehicle.The rod 9 a is able to slide with respect to the body 9 b under theeffect of the gases generated one or several tablets 10 a, 10 b, 10 c ofgas-generating composition.

A specific pyrotechnic squib (not shown) can individually initiate eachcomposition tablet. The tablets are isolated from one another so thatinitiating one of them does not in turn initiate the others.

Each tablet can thus be positioned in a gas-tight case (not shown)having a lid that can be fractured by the gas pressure.

An electronic control system 11, integral with the vehicle, receives thesignals transmitted by impact sensors 12 a, 12 b, 12 c that areadvantageously integral with the rigid support 3 or else with the shell2 itself. The impact sensors are evenly spaced over the length of thebumper for reasons that will be explained after.

A sensor (12 a, 12 c) can, for example, be placed in the vicinity ofeach bumper end and another sensor 12 b in the median part.

The impact sensors will, for example, be constituted by fracture pinsassociated with electromechanical or piezoelectric contacts. These willbe assembled such that fracturing the pin (occurring during impact)causes the closure or opening of the contact.

Sensors in the form of electrical contacts integral with the bar 3 canalso be adopted that are fractured when said bar undergoes a certainlevel of strain. Stress gauges or contactor sensitive to a certain levelof deceleration the vehicle can also be used.

The signals transmitted by sensors 12 a, 12 b, 12 c are processed by thesystem 11 that incorporates a suitable algorithm allowing the initiationof one or several tablets 10 a, 10 b, 10 c to be controlled.

Advantageously, the control system 11 will also ensure the activation ofthe other safety systems of the vehicle (inflation of driver and/orpassenger airbags, seat belt pretensioners, . . . ).

Such a bumper operates as follows.

Classically, the bumper shell structure enables it to absorb a shockoccurring at a speed of less than 4 km/h. The rigidity of block 19 alsoallows the shock received by the shell to be spread over the wholestructure and notably over the full length of the rigid support 3.

When the speed exceeds 4 km/h, the shell 2 deforms and crushes theshock-absorbing blocks 19, that thus absorb part of the energy ofimpact.

Using such a shock-absorbing material it is possible for the energycorresponding to an impact occurring at a speed less than or equal to 15km/h to be absorbed.

Sensors 12 a, 12 b , 12 c detect impact occurring at speeds of over 15km/h.

Further to their detection, the control system 11 controls theinitiation of one or several tablets 10 a, 10 b, 10 c of gas-generatingcomposition. The pyrotechnic actuators 9 are thus activated and allowthe extra energy from the impact received to be absorbed.

Because of the presence of several impact sensors 12 a, 12 b, 12 cspaced along the length of the bumper, the control system is able tolocate the position of the impact received by the vehicle with respectto its median axis 14.

Indeed, in the case of an offset impact, and according to the sensortechnology used, the signal transmitted by the impact sensor that isclosest to the point of impact will be the strongest, or else the impactsensor closest to the point of impact will fracture the first.

At least two impact sensors will be provided, one on either side of themedian axis 14. Each of these sensors will thus more easily detect animpact occurring on one side or the other of the median axis, thus onthe right or left of the vehicle.

The control system 11 will then control the initiation of a greaternumber of tablets 10 for the pyrotechnic actuator 9 closest to the pointof impact (for example, the three tablets 10 a, 10 b, 10 c of theclosest actuator and a single tablet for the one that is furthest away).

The effort produced by the closest actuator to the point of impact willthus be greater than that produced by the actuator that is furthestaway. Such an arrangement allows the absorption of the shock to beadapted according to the position of impact with respect to the medianaxis 14 of the vehicle thereby preventing the vehicle from wrappingaround an offset obstacle.

By way of a variant, it is possible for impact sensors to be providedthat allow several impact speeds over 15 km/h to be differentiated andconsequently a different number of gas-generating composition tablets tobe initiated according to the violence of impact.

The higher the speed of impact, the more gas-generating compositiontablets will be initiated.

By way of a variant, it is possible for shock-absorbing materials to beprovided other than block of hollow balls 19, for example porousmaterials.

FIGS. 2a and 2 b show a second embodiment of a bumper 1 according to theinvention.

In accordance with this embodiment, the shell 2 delimits an inner volume7 inside which there is a casing 6 made of an elastic material, forexample rubber, that can be reinforced. The casing 6 is fastened tosupport 3, for example by bonding or duplicate moulding, and has anopening at which a pyrotechnic gas generator 8 is placed in a gastightmanner. In the starting position shown in FIGS. 2a and 2 b, the casing 6is pre-inflated under moderate pressure and thus substantially fills thewhole inner volume of the shell 2. Such an arrangement is intended toreduce the reaction time of the device according to the invention, thopyrotechnic generator can in this case ensure the pressurization of thecasing without having to inflate it completely.

The thickness of the casing will he chosen sufficient to ensure aconstant gas pressure without fracturing of around 1 to 2 Mega Pascals.A rubber casing of around 8 mm in thickness will be adopted, forexample.

The gas generator is of a known type, notably used for inflatingautomobile airbags. It can incorporate around 10 grams of a propellant(butalane a propellant including ammonium perchlorate, Al-powder and abinder as polybutadiene) or nitride type and will he initiated by meansof a pyrotechnic squib.

According to this embodiment of the invention, each arm 5 also comprisesa pyrotechnic actuator 9 that has a rod 9 a fastened to the rigidsupport 3 and a body 9 b linked to the vehicle. The rod 9 a is able toslide with respect to the body 9 b under the effect of the gasesgenerated by one or several gas generating tablets 10 a, 10 b, 10 c.

Each composition tablet can be initiated individually using a specificpyrotechnic igniter (not shown). The tablets are isolated from oneanother so that initiating one of them does not cause the initiation ofthe others. Each tablet can thus be placed inside a gas-tight case (notshown) fitted with a lid that can be fragmented by the gas pressure.

An electronic control system 11, integral with the vehicle, receives thesignals transmitted by the impact sensors 12 a, 12 b, 12 c that will beadvantageously integral with the rigid support 3 or else with the shell9 itself. The impact sensors are evenly spaced over the length of thebumper for reasons that will be specified later.

A sensor (12 a, 12 c) can be placed, for example in the vicinity of thebumper ends and another sensor (12 b) at the median part.

The control system also receives the signal transmitted by adeceleration contactor 13, for example inertia-bed.

The impact sensors will be formed, for example, by fracture pinsassociated with electromechnical or piezoelectric contacts. These willbe assembled such that fracturing the pin (occurring during impact)causes the closure or opening of the contact.

Sensors in the form of electrical contacts integral with the bar 3 canalso be adopted that are fractured when said bar undergoes a certainlevel of strain. Stress gauges or contactors sensitive to a certainlevel of deceleration greater than that of contactor 13 can also beused.

The signals transmitted by sensors 12 a, 12 b, 12 c are processed by thesystem 11 that incorporates a suitable algorithm allowing the initiationof one or several tablets 10 a, 10 b, 10 c and/or the gas generator 8 tobe controlled.

Advantageously, the control system 11 will also ensure the activation ofthe other safety systems of the vehicle (inflation of driver and/orpassenger airbags, seat belt pretensioners, . . . ).

Such a bumper operates as follows.

Classically, the bumper shell structure enables it to absorb a shockoccurring at a speed of less than 4 km/h.

When the speed exceeds 4 km/h, the deceleration contactor 13 isactivated and the control system 11 causes the gas generator 8 to beinitiated.

Since the casing 6 is already pre-inflated it is almost instantaneouslypressurized by the gases generated by the generator 8 (pressurizationtime of around 5 ms). It still occupies the whole of the inner volume ofthe shell 2.

The pressurised casing allows the shock received by the shell to bespread over the whole structure and notably over the length of the rigidsupport 3. It also allows the deformations due to the impact, and thusthe shock, to be absorbed.

Such an operating mode is controlled for a vehicle speed upon impact ofbetween 4 km/h and 15 km/h.

The casing proposed by the invention is more effective and more reliablethan that disclosed in document U.S. Pat. No. 5,651,569. Indeed, thecasing is only pressurized upon impact, and there can therefore be noreduction in gas pressure during the normal operation of the vehicle.Moreover, the pressure developed can be much greater than that obtainedby mere pre-inflation. This results in great shock-absorbingcapabilities.

Sensors 12 a, 12 b, 12 c detect an impact occurring at a speed of over15 km/h.

Further to this detection, the control system causes the initiation ofone or several of the gas-generating tablets 10 a, 10 b, 10 c. Thepyrotechnic actuators 9 are thus activated and allow the extra energyfrom the impact received to be absorbed.

Because of the presence of several impact sensors 12 a, 12 b, 12 cspaced along the length of the bumper, the control system is able tolocate the position of the impact received by the vehicle with respectto its median axis 14.

Indeed, in the case of an offset impact, and according to the sensortechnology used, the signal transmitted by the impact sensor that isclosest to the point of impact will be the strongest, or else the impactsensor closest to the point of impact will fracture the first.

At least two impact sensors will be provided, one on either side of themedian axis 14. Each of these sensors will thus more easily detect animpact occurring on one side or the other of the median axis, thus onthe right or left of the vehicle.

The control system 11 will then control the initiation of a greaternumber of tablets 10 for the pyrotechnic actuator 9 closest to the pointof impact (for example, the three tablets 10 a, 10 b, 10 c of theclosest actuator and a single tablet for the one that is furthest away).

The effort produced by the closest actuator to the point of impact willthus be greater than that produced by the actuator that is furthestaway. Such an arrangement allows the absorption of the shock to beadapted according to the position of impact with respect to the medianaxis 14 of the vehicle thereby preventing the vehicle from wrappingaround an offset obstacle.

By way of a variant, it is possible for impact sensors to be providedthat allow several impact speeds over 15 km/h to be differentiated andconsequently a different number of gas-generating composition tablets tobe initiated according to the violence of impact.

The higher the speed of impact, the more gas-generating compositiontablets will be initiated.

By way of a variant, it is possible for a casing 6 to be provided thatis not pre-inflated in its starting position.

As for the previous embodiment, this casing will be pressurized byinitiating the gas generator 8. This variant of the invention has alonger reaction time and is substantially less effective than the onepreviously described. It is, however, more effective that the onedescribed in patent U.S. Pat. No. 5,651,569, as the pressure obtained isgreater and invariable over time.

By way of a variant, it is also possible for a bumper to be made inwhich the casing 6 and shell 2 form one element. All this requires isthe provision of a bottom wall closing off the shell and therebydelimiting a gastight inner volume pressurised by at least one gasgenerator.

FIG. 3 shows a bumper 1 according to a third embodiment of theinvention.

This embodiment differs from the previous one in that the single casing6 in FIG. 2a is replaced by three casings 6 a, 6 b, 6 c (that can alsobe made in the form of a single casing having inner partitionsdelimiting three inflatable chambers 15 a, 15 b, 15 c).

Each chamber 15 a, 15 b, 15 c can be pressurized by a specific gasgenerator 8 a, 8 b, 8 c whose initiation is caused by the control system11.

Several impact sensors 12 a, 12 b, 12 c are placed along the bumper andenable the impact received to be located with respect to the median axis14 of the vehicle.

According to the location of the impact, the control system willinitiate one or other of the gas generators 8. It can also initiate allthe generators if the violence of impact detected reaches a certainlevel.

The arms 5 of this bumper are identical to those described withreference to the previous Figures.

FIG. 4 shows a variant embodiment of the bumper according to theinvention, wherein the casing 6 in FIG. 1a is replaced by two casings 6a and 6 b each delimiting a chamber 15 a, 15 b that can be pressurizedby means of a specific gas generator 8 a, 8 b. These two casings canalso be formed by a single casing incorporating an inner partitiondelimiting the two chambers 15 a, 15 b.

FIG. 5 shows another variant embodiment in which the casing 6incorporates two longitudinal partitions 18 delimiting three innerchambers 15 a, 15 b and 15 c. Each chamber can be pressurised by aspecific gas generator 8 a, 8 b and 8 c. Such an arrangement allows thereaction of the device to be adapted depending on the height of theimpact and its energy.

In any case, partitioning the chambers allows the casings to bepressurised more quickly.

The device according to the invention can be adapted both for a frontand rear bumper.

What is claimed is:
 1. A bumper (1) for a vehicle, said bumpercomprising a shell (2) including shock-absorbing means for dampingimpacts, a rigid support (3), two arms (5), a control system (11), andat least one sensor selected from the group consisting of impact sensorsand deceleration sensors (12 a, 12 b, 12 c), said shell (2) beingattached to the rigid support, and the rigid support being linked to thevehicle by the two arms, said arms each comprising a pyrotechnicactuator (9) for exerting force on said shell, each said actuator beingelectrically connected to said control system (11), said control systembeing electrically connected to said at least one sensor (12 a, 12 b, 12c), and each pyrotechnic actuator (9) incorporating at least twogas-generating powder tablets (10 a, 10 b, 10 c) each tablet capable ofbeing primed individually by the control system (11) to energize theactuator responsive to at least two impacts of differing intensities. 2.The bumper according to claim 1, further comprising at least one meansfor determining position, wherein the control system (11) iselectrically connected to the means for determining position forreceiving a signal indicative of the point of an impact received by thevehicle with respect to a median axis (14) of the vehicle, so that thecontrol system (11) activates the actuator nearest the point of impact,said activation producing an effort greater than the effort produced byactivation of an actuator located furthest from the point of impact,said effort being a force exerted on the shell.
 3. The bumper accordingto claim 2, wherein the means for determining position comprises atleast two impact sensors (12 a, 12 b) one of which is disposed on eachside of the median axis (14) of the vehicle.
 4. The bumper according toclaim 1, comprising at least one block (19) of shock-absorbing materialbetween the rigid support (3) and the shell (2).
 5. The bumper accordingto claim 4, wherein each shock-absorbing block (19) is formed of hollowballs arranged in a matrix of plastic material, said balls configured tobe crushed under impact to the shell.
 6. The bumper according to claim1, wherein the means for determining position comprises at least oneinner volume in the shell (2) configured to be pressurized by acompressible fluid supplied by a generator (8) capable of beinginitiated by the control system (11) linked to said at least one sensor(12, 13).
 7. The bumper according to claim 6, wherein the pressurizablevolume comprises at least one casing (6, 6 a, 6 b, 6 c) made of anelastic material selected from the group of materials consisting ofreinforced elastic materials and non-reinforced elastic materials, saidcasing being arranged between the rigid support (3) and the shell (2).8. The bumper according to claim 6, wherein the casing (6, 6 a, 6 b, 6c) comprises partitions selected from the group consisting of partitionsincluding longitudinal and transversal partitions, said partitionsforming at least two inner cavities (15 a, 15 b) in the casing.
 9. Thebumper according to claim 6, wherein the at least one fluid generator isa pyrotechnic gas generator (8).
 10. The bumper according to claim 9,wherein the control system (11) is connected to initiate a predeterminedgas generator according to an impact parameter selected from the groupconsisting of impact and deceleration parameters.